14北京大学分析化学03酸碱

OutlineforPartIII•PreliminaryPreparation–Aqueoussolutionsandchemicalequilibria–Effectofelectrolytesonchemicalequilibria–Solvingequilibriumproblemsforcomplexsystems–Thecompositionofacid/basesolutionasafunctionofpH–CalculatingpHofacid/basesolution–Acid-baseBuffer•Neutralizationtitrations–Indicatorsforneutralizationtitrations–Strongacid-basetitration–TitrationofHAbystrongbase–TitrationofAbystrongAcid–StepwisetitrationofH2Abystrongbase–TitrationoftotalH2Abystrongbase–CalculationoftitrationError–ApplicationexamplesAqueoussolutionandChemicalEquilibria•Thechemicalcompositionofaqueoussolution–Classifyingsolutionsofelectrolytes–Acidsandbases–Autoprotolysis–Strengthsofacidsandbases•Chemicalequilibrium–Theequilibriumstate–Equilibriumconstantexpressions–Typesofequilibriumconstantsencounteredinanalyticalchemistry–ApplyingtheIon-productconstantforwater–––ApplyingsolubilityApplyingsolubilityApplyingsolubility---productconstantproductconstantproductconstant–Applyingacid-basedissociationconstantsClassificationofElectrolytes•Strong:ionizeessentiallycompletelyinasolvent;conductivityisgood•Weak:ionizepartially;conductivityispoorStrongWeakInorganicacids:HNO3,HClO4,HaSO4,HCl,HI,HBr,HClO3,HBrO3Manyinorganicacids:H2CO3,H3BO3,H3PO4,H2S,H2SO3Alkaliandalkaline-earthhydroxidesMostorganicacidsMostsaltsAmmoniaandmostorganicbasesHalides,cyanides,andthiocyanatesofHg,Zn,andCdAcidsandBases•Anaciddonatesprotons;abaseacceptsprotons•Anaciddonatesprotonsonlyinthepresenceofprotonacceptor(abase)-conjugatebase.Likewise,abaseacceptsprotonsonlyinthepresenceofaprotondonor(anacid)-conjugateacid.•Asubstanceactsasanacidonlyinthepresenceofabase,andviceversa.•Manysolventsareprotondonorsorprotonacceptorsandcanthusinducebasisoracidicbehaviorinsolutesdissolvedinthem.Acids酸andBase碱(Brønsted-LowryTheory)Acid⇋ConjugateBase共轭碱+Proton质子ProtondonorProtonacceptorProtonHAc⇋Ac-+H+NH4+⇋NH3+H+HCO3-⇋CO32-+H+H6Y2+⇋H5Y++H+InGeneral:HA⇋A-+H+Acid-BaseEquilibriumHalfreaction1:HAc⇋Ac-+H+Halfreaction2:H++H2O⇋H3O++Ac-___________________________________Totalreaction:HAc+H2O⇋Ac-+H3O+SimplifiedExpression:HAc⇋Ac-+H+Example:DissociationofHAcinwater酸碱反应的实质是ProtonTransfer质子转移AmphiproticSpecies•Speciesthatpossessbothacidicandbasicproperties•Zwitterion:Aspeciesthatbearsbothapositiveandanegativecharge•Wateristheclassicexampleofanamphiproticsolvent•AmphiproticsolventsbehaveasacidsinthepresenceofbasicsolutesandbasesinthepresenceofacidicsolutesAutoprotolysisH2O+H2O⇋H3O++OH-(25℃)14w(H)(OH)1.0010Ion-productConstantKaa+−−=⋅=×p237Why[H2O]notinKw?Amphiproticsolventsundergoself-ionization(autoprotolysis)toformapairofionicspeciesCH3OH⇋CH3OH2++CH3O-HCOOH⇋HCOOH2+HCOO-NH3⇋NH4++NH2-DissociationofaWeakAcid/Base+-ab-(H)(A)(HA)(HA)(OH)(A)aaKaaaKa−⋅=⋅=−HA+H2O⇋A－+H3O+A-+H2O⇋HA+OH－awbppp14.00(25C)KKK+==°StrengthofAcidsandBasesPerchloricacidandhydrochloricacid¾Differentiatingsolvent区分溶剂anhydrousaceticacid¾Levelingsolvent拉平溶剂-H2OH3A⇋H2A-⇋HA2-⇋A3-DissociationofPolyproticAcidspKb1=14.00–pKa3pKb2=14.00–pKa2pKb3=14.00–pKa11bK2bK3bK2aK3aK1aKH++OH-⇋H2OH++A-⇋HAOH-+HA⇋H2O+A-14.00tw110KK==bw()KKtb1KK=ta1KK=aw()KKNeutralization(Titration)ReactionKt—TitrationConstantTheEffectofIonicChargesonEquilibriaTheeffectofaddedelectrolyteonequilibriaisindependentindependentofthechemicalnatureoftheelectrolytechemicalnatureoftheelectrolytebutdependsonapropertyofthesolutioncalledtheionicstrength(ionicstrength(I,I,μμininSkoogSkoogbookbook).).Specifically,inthesolutionwithIof0.1mol/Lorless,theelectrolyteeffectsisindependentofthekindofionsanddependentonlyontheI.I(μ)=½([A]ZA2+[B]ZB2+[C]Zc2+…)A,B,andC:Ionsinslution[A],[B],and[C]:ConcentrationsZA,ZB,andZc:ChargesEffectofChargeonIonicStrengthTypeElectrolyteExampleIonicStrength1:1NaClc1:2Ba(NO3)2,Na2SO43c1:3Al(NO3)3,Na3PO46c2:2MgSO44cEffectofConcentrationTheEffectofElectrolytesonChemicalEquilibria[X]aγ=a:activity活度γ:activitycoefficient活度系数Propertiesofγ:1.AsI→0,γ→1,a→[X]andK′→K2.Forunchargedmolecules:γ≈13.Forsolvent:a=14.ForgivenI,theγofionsofthesamechargesareapproximatelyequal.5.SetI,Charge↗,γ↘6.SetCharge,I↗,γ↘Debye-HückelEquationforCalculationofActivityCoefficients20.509lg0.1)1iiZIIBaIγ−=+（whenoConstant:B=3.28(25C),a:EffectiveDiameterofthehydratedioninnanometers(nm)与温度、介电常数有关离子体积参数单位：Acid/BaseDissociationConstantsinKa活度常数,浓度常数,and混合常数HAc⇋H++Ac-[]+-aaca(H)(Ac),p4.76(HAc)HAc(H)(Ac)(HAc)HAc(HAc)(H)(Ac)aaKKaaaKaγγγ+−+−+−⋅==⎡⎤⎡⎤⋅⎣⎦⎣⎦==⋅⋅ca(0.1,(H)0.826,(Ac)0.770)p4.56IKγγ+−====a(H)(Ac)Kγγ+−=⋅caKMaK()[]MaaHAc(H)(Ac)(HAc)HAc(HAc)(Ac)(Ac)aKaaKaγγγ+−+−−−⎡⎤⋅⎣⎦==⋅=Map4.65(0.1)KI==CMaaaHAc:KKKKa:ThermodynamicConstant(只与t有关):ConcentrationConstant(与t,I有关):MixedConstant(与t,I有关)caKMaK[][][]-aHAHA(HA)HAAHHxcK++===⎡⎤+⎣⎡⎤⎣⎦⎡⎤+⎣⎦⎦[]----aaAA(A)HAAHxcKK+⎡⎤⎡⎤⎣⎦⎣⎦===⎡⎤+⎣⎡⎤+⎣⎦⎦RelativeEquilibriumConcentration-Fraction,x弱酸(碱)形体分布(HA)(A)1[HA](HA),[A](A)xxcxcx+==⋅=⋅HA“α”SkoogBookExampleCalculatex(HAc)、x(Ac-),whenthepHofsolutionis4.00and8.00aaapH=4.00,(HAc)0.85(Ac)HHH0.15KKxKx−+++===⎡⎤⎣⎦⎡⎤+⎣⎦⎡⎤+=⎣⎦ForHAc,Ka=1.75×10-5pH=8.00,x(HAc)=5.7×10-4,x(Ac-)≈1.0pHx(HA)x(A-)pKa-2.00.990.01*pKa-1.30.950.05pKa-1.00.910.09**pKa0.50